1. Field of the Invention
The present invention relates to a laser apparatus, and more particularly, to a pulse laser apparatus that may adjust a laser pulse width and output pulse energy.
2. Discussion of Related Art
Recently, lasers have been widely used in medical treatment, and medical treatment apparatuses using such lasers have been used in dermatological, ophthalmic, dental, and surgical operations. In general, the laser treatment apparatus in a dermatology clinic is used to treat a lesion such as a skin disease and a blood vessel disease by radiating a laser having a uniform wavelength and intensity. Various types of lasers are used for treatment in a dermatology clinic. A Q-switched Alexanderite laser (operating at 755 nm) is mainly used to remove a spontaneous dermatological pigmentation or tattoo. A long pulse ruby laser is used to remove hair, and an Nd:YAG laser (operating at 1060 nm), a CO2 laser (operating at 10.6 μm) and an argon laser (operating in the range of 488 nm to 514 nm) are used to treat a dilated vessel.
Specifically, in a dermatology clinic, laser treatment apparatuses are used to solve various dermatological problems such as mottled spots, dilated vascular disorders, and pigmentation disorders including tattoos. The laser treatment apparatuses locally apply heat to raise a temperature such that component proteins may be denatured or a pigment may be dispersed. In this case, a pulse width of the radiated laser light is a critical factor. When the pulse width is too long, absorbed heat is dispersed into adjacent tissues such that heat may not be selectively applied to a desired degree. However, when the pulse width is too short, light absorption chemical substances such as a hemoglobin or a tattoo color particle is heated and vaporized too quickly. Accordingly, a suitable pulse width needs to be matched with a thermal diffusion time of a target point. A phenomenon in which a target generates heat by absorbing radiated light is referred to as a photothermal effect. A light source optimized for this is a Q-switched laser having a pulse width of several tens to hundreds of nanoseconds.
According to recent clinical trials, it can be seen that a picosecond pulse generated through mode locking allows for effectively removing a tattoo or pigmentation disorder and preventing a scar, as compared to a nanosecond pulse generated through an existing Q-switching. The picosecond pulse may be applied more shallow to a small area by using a photomechanical effect, which can be applied more selectively than the photothermal effect, thus reducing a treatment time and minimizing a scar or side effect. However, in order to perform the mode-locking for acquiring a short picosecond pulse, a separate fast optical modulator is needed in addition to a Q-switch modulator.
FIG. 1 is a basic block diagram illustrating a mode-locked and Q-switched Alexanderite laser apparatus according to conventional technology.
Referring to FIG. 1, a laser apparatus include a resonator that generates a laser, and the resonator includes a first mirror, a second mirror, a gain medium, and two optical modulators (a first optical modulator and a second optical modulator) arranged therein along an optical axis.
One of the first mirror and the second mirror disposed at both ends of the resonator is a fully reflective mirror with total reflection, and the other is a partially reflective mirror. Laser light generated in the resonator is output through the partially reflective mirror. The laser pulse from the gain medium to the second mirror passes through the second optical modulator and is reflected by the second mirror, and then passes through the second optical modulator, the gain medium, and the first optical modulator to the first mirror. In this case, the second optical modulator serves to generate a mode-locked pulse, and the first optical modulator serves to generate a Q-switched pulse. The laser light oscillated within the resonator is output to the outside along an output path when the laser light has a desired magnitude.
It is very useful to appropriately change a laser pulse width depending on a type or state of a lesion in the clinical environment. However, conventional mode-locked laser treatment apparatuses generally have a fixed pulse width of a laser for treating skin pigmentation or injury, and thus it is difficult to change the pulse width in any desired way.
In order to perform mode-locking and Q-switching in the conventional technology, the laser resonator should include two optical modulators. In particular, an electro-optic modulator, which is widely used, requires a high-cost and complicated electric circuit because a driving signal obtained by modulating a high voltage of several kV in nanoseconds should be used to drive the electro-optic modulator.